1. Technical Field
The present invention relates to an ink-jet printer which records on a recording paper sheet by high-speed discharge of ink droplets from an ink-jet nozzle onto the paper sheet.
2. Description of the Prior Art
Of various recording systems, ink-jet printing very useful for a printer a copying machine or a word processor. Ink-jet printing system is a nonimpact recording which generates substantially no noise during recording and which is capable of high-speed recording. An ink-jet printing system does not require any special processing for fixing on a regular printing paper sheet.
Various improvements have been proposed and have been put into practice in ink-jet printing systems, and further developments are still being made.
In an ink-jet printing system, small ink droplets are discharged in accordance with various principles and are attached onto a recording medium for recording. An ink-jet printer generally comprises an ink-jet head for forming ink droplets, ink supply means for supplying ink to the ink-jet head, recovery processing means for recovering and processing the ink which is exhausted from the head in the recording mode, and clogging remedy processing means for eliminating clogging of an ink-jet nozzle or an ink channel of the head.
Although the ink-jet printing system is an excellent recording system with a simple configuration, it is also subject to some problems.
The first problem is clogging of the ink-jet nozzle. Two factors can be considered responsible for clogging of the ink-jet nozzle. The first factor is evaporation of an ink solvent from the end of the ink-jet nozzle and a resultant increase in the ink viscosity at the distal end of the nozzle. Thus, the ink cannot be properly discharged.
The second factor is introduction of fine dust or the like into the ink. The introduced dust clogs the ink-jet nozzle.
Another problem is associated with introduction of air bubbles into the ink. When such air bubbles in the ink are supplied into the ink-jet nozzle, the discharge energy is absorbed by the bubbles and the ink cannot be discharged. Alternatively the ink droplets are dispersed, causing so-called splashing.
In order to solve these problems, generally a clogging remedy processing means, including a pump means, is used. The pump means can be included at two different positions in the ink flow circuit. First, the pump means may be located between the ink-jet head and the ink tank. The pump compresses the ink in the ink tank and forces it toward the head. Highly viscous ink, and dust and air bubbles in the ink in the nozzle and channel are exhausted from the distal end of the nozzle as waste ink.
Second, the pump means may be connected to the distal end of the ink-jet nozzle. The ink is drawn by suction from the distal end of the nozzle so as to draw out as waste ink the highly-viscous ink, and fine dust and air bubbles in the ink in the head or channel for supplying ink to the head.
When the remedy operation is performed by the remedy processing means, the nozzle surface is covered with the waste ink which has leaked out from the nozzle.
In the case of a head nozzle wherein an array of a plurality of nozzles is formed on the nozzle surface, if the ink exhausted from an upper nozzle covers the lower nozzle, the lower nozzle may fail to discharge ink during subsequent recording. When ink is not removed from a covered nozzle for a long period of time, the ink solvent evaporates. Then, the remaining dye or the like forms a thin film on the nozzle end, and the nozzle covered with such a thin film of the ink cannot discharge ink during recording.